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Thread: Half Bridge vs Full bridge SMPS

  1. #1

    Half Bridge vs Full bridge SMPS

    Hi.
    The subject of my engineering work is the design of smps 500W for audio amplifier.
    I do not know what to choose topology (half vs full bridge). Personally, I would like to build a full bridge smps

    I would like to ask you what are the advantages of a full bridge over the half bridge,I think about efficiency, power distortion..etc.
    I will be grateful for your answers

  2. #2
    .... Silvio's Avatar
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    @Robson132
    Well in theory half bridge is suitable up to 500w but I got 1200 out of a half bridge smps. I think if you use half bridge is well suited to the power level you want for audio purpose. The duty cycle is more or less 60% for audio to get to the power needed. Regarding efficiency I got 90% or better in my prototypes.

    Full bridge is usually used for more power above 1000 watts. Having full bridge needs more winding on the trafo and the circuit will be more complicated and more care is needed. Efficiency tends to be better with full bridge as less current is needed for the same power due to the primary voltage is double. If its your first time building a SMPS then I suggest you start with a simple one with no feedback. Unregulated is suitable for audio purposes. As far as distortion usually the frequencies used in smps are far higher than the audio frequencies and are not usually heard, however good EMI filtering and shielding is needed.

    I suggest you stay under 100Khz as more care is needed in the layout and stray coupling and inductance try to get in the way. Switching losses also play their part in high frequencies. You can take a look at my smps which is published here called a Audio smps 700w (IR2153). I suggest you take a look at the tread and take some ideas. There is also the pdf file available in post #13. There are also other smps you can build from this site.

    Regards Silvio

  3. #3
    Thank you for your answer.

    I'm designing a half bridge smps. In this topic I would like to get help if needed

  4. #4
    .... Silvio's Avatar
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    Go ahead but please show schematic so that we can help you out.

    Regards Silvio

  5. #5
    How to calculate the required input capacitance?

  6. #6
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    @Robson
    If using 400v capacitor then 1uF per watt. If using 200v caps then 2uF per watt. These are minimum ratings double the value is good 3 times the value is an overkill.

  7. #7
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    is it possible to draw a 2,000 watts smps from half bridge design ? i'm planning to use 24A mosfet in the primary side but still half bridge ? I wonder if i can withdraw 2KW smps with that and with EE55 ferrite core.

  8. #8
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    Hi Ruzzell,

    What exactly are your intentions for this power supply? is it for audio purpose? I guess you can peak 2000 watts with an EE55 core but it will be a question of the duty cycle needed. I guess at 50% duty cycle you may get away with it and also some added cooling will be necessary.

    Your input capacitance have to be strong and you will need around 2 to 3000uf X 400v across the 320v rail. On the output on the other hand you will need around 5 to 6000uF on each rail assuming an output voltage of 100v -0-100v.

    Regarding your switching devices well I guess you will be better off using parallel switchers on the half bridge say 2 X irfp460 for high side and 2 more in parallel for the low side. One other thing is that you have to have a strong signal arriving at the gates of the mosfets and a current amplifier has to be added with your driver

    Half bridge is not really suited for such high power and full bridge is more suited. Full bridge is a bit more complicated and not so easy for the inexperienced. I do not know what is your experience is in SMPS but if you have never built a high power smps it will be somewhat different from a normal one of say 500w. Stray inductances tend to go everywhere and couple themselves in other signal lines which may disturb them and giving false triggering which may lead to catastrophic not to mention spectacular surprises.
    Lastly EMI and bad power factor will be at its best.

    Regards Silvio

  9. #9
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    thanks for the info sir . I have experience and success in building small smps that is about 900w for audio purposes. I think I should double my mosfets in high side and in the low side and also with totempole. My mosfets was driven by ir2110 ic. My primary capacitor is 400v 2,200uf and output capacitor of 7 pairs 100v 680uf on the secondary output. Target voltage is +/- 90v dc. I will try to proceed with half bridge design because i aleady wounded my trafo for half bridge design. I wish for luck with my project . By the way i doesn't still have an oscilloscope because it was expensive on my part. I just relay with the existing designs from this forum. I wish I could succeed with my project. I will update you sir once I am done buiding it and make some load test. Thanks a lot

    Regards
    Ruzzel Rotao

  10. #10
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    Hi Ruzzel, It is good that you already wound the trafo I guess you can still use the IR 2110 to drive the fets. You can use 10 ohms resistor with each fet IR 2110 can take 4.7 ohms with one fet so with 2 fets you can use 10 ohms on the gates. I want to know what frequency are you designing your smps. Try to stay below 100Khz I think between 50Khz and 70Khz is good. Just let know the number of turns you did for your transformer primary and secondary. Please also tell me the core material you have in the trafo.

    Your choice for input and output capacitance seems to be enough

    Lastly keep the traces from the IR2110 to the mosfets as short and wide as possible. keep also the traces from the driver to IR short to eliminate stray coupling. Decouple the low voltage supply rails at various points along the path to the pwm chip and also near the chip.

    Without oscilloscope is a bit difficult at times as you cannot see what is happening. Be careful and wear glasses when switching on first time.

    Good luck Silvio
    Last edited by Silvio; 01-27-2018 at 03:57 PM.

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